Jay-Z and Kanye West and performing at Yankee stadium. Photo: WireImage

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Last August, while Kanye West was completing his fifth solo album, “My Beautiful Dark Twisted Fantasy,” he was already tweeting about his next project: A five-song EP with Jay-Z titled “Watch the Throne.”

Rap fans didn’t hold their breath. After all, the genre is littered with aborted all-star projects, from Dr. Dre and Ice Cube to Common and Q-Tip. But this partnership didn’t seem so far-fetched. Jay-Z is an eager collaborator and already pulled off full-length albums with Linkin Park and R. Kelly. Plus, he maintains a good relationship with West — they share a competitive student-teacher dynamic — and the pair were on a creative roll following collaborations on “My Beautiful Dark Twisted Fantasy” (“Monster” and “So Appalled”).

Jay-Z and West quickly got to work, and the project morphed into a full-length album. Now, after a secretive recording process that spanned four continents, “Watch the Throne” will be exclusively available on iTunes tomorrow.

In true rock-star fashion, West and Jay-Z recorded in mansions and grandiose hotels in London, Paris, Sydney and Abu Dhabi. Those sessions attracted plenty of celebrities — including Russell Crowe and Givenchy creative director Riccardo Tisci, who designed the album’s artwork — but produced little material that made the final cut.

The first song released from the album, “H.A.M.,” turned out to be another bump in the road. Produced by Lex Luger, hip-hop’s beat-maker of the moment, “H.A.M.” was a chaotic mess that was greeted with radio silence after its splashy January debut.

The longtime friends then regrouped. Later that month, they rented a block of rooms in SoHo’s Mercer Hotel and invited a select group of producers and artists. “There was music going on in every room,” says Chauncey “Hit Boy” Hollis, who produced the track “N – – – – s in Paris.” “I had a room where I was cranking out beats, and then I’d go into the main room with Jay and [Kanye] and play beats for them. Kanye is really hands-on. I would come in with a beat and he’d be like, ‘Take this out, slow it down.’ It would make it sound 100 times better. Jay would then mumble different flows to the beat.”

After a proposed March release date fell through, Internet scuttlebutt said the project might be scrapped. A rumored July Fourth release date also came and went. Then on July 17, Hot 97 DJ Funkmaster Flex premiered “Otis” on his nightly show. Over an expertly chopped sample of Otis Redding’s “Try a Little Tenderness,” Jay-Z and Kanye, now dubbed the Throne, traded sharp verses about their conspicuous consumption. It immediately became a contender for song of the summer.

The single hit with increased effect because of the secrecy around the project. The duo avoided leaks by recording together (which limits the amount of file transfers) and keeping a tight inner circle.

“I haven’t even heard the records,” says producer Sham “Sak Pase” Joseph, who worked on two of the album’s tracks. “I’m going to be in line buying a copy because I want to hear the finished work. I’m as much in the dark as everyone else is.”

But if they succeeded at security, the frenemies flopped when it came to promoting the album. Last week, Page Six reported that they feuded over their tour and had to push its opening date back a month. (NYC dates are now at the Izod Center on Nov. 5 and 6.)

Jay-Z moved to dispel rumors that he’s “fed up with West’s antics” during an interview with Hot 97’s Angie Martinez. “Yes, we get on each other’s nerves, but that’s part of pushing each other,” he said. “The people who have a problem with Kanye or myself are the people that are complacent in life.”